Coatings, paints, caulks and adhesives are often subject to weathering conditions that shorten their useful lifetimes. In addition, they can be subjected to mechanical impacts and abrasions that create damage areas in the surfaces that serve as a starting points for failure mechanisms. Fluoropolymers are known for their outstanding weathering resistance in the architectural coatings area, and in films used in outdoor applications such as for solar panel components. Improvement of their mechanical properties can further extend their utility in these and other areas, such as in industrial coatings, caulks and adhesives used in locations requiring good weathering and mechanical properties. An approach to improving the mechanical properties of fluoropolymer coatings, paints, caulks and adhesives is to modify the weathering-resistant fluoropolymer with other polymers that improve mechanical properties. The degree and nature of mixing different polymers are important parameters in the final properties of the mixture. By making the mixtures using a seeded emulsion polymerization process, very intimate mixing can be achieved, and the waterborne emulsion process provides an environmentally sound material that can be used to make the weatherable coatings, paints, caulks and adhesives with improved mechanical properties.
Fluoropolymer hybrid compositions are described in U.S. Pat. No. 5,349,003 with the optional polymerization of some immiscible monomer in a single stage acrylic polymerization process. Two-stage acrylic or methacrylic polymerizations were not described and no mention of glass transition temperatures or low temperature mechanical performance was made. The fluoropolymer was specified as a copolymer made with vinylidene fluoride and tetrafluoroethylene monomers, or a terpolymer made with vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene monomers. A copolymer of vinylidene fluoride and hexafluoropropylene was not described.
A seeded emulsion polymerization process was used in US 2004/0019145 A1 to make fluoropolymer hybrid compositions using a single stage acrylic or methacrylic polymerization on a fluoropolymer seed latex. Two-stage acrylic or methacrylic polymerizations were not presented. Despite describing a large list of alkyl groups that could be present in the acrylic or methacrylic copolymers, no mention was made of immiscibility and its use to improve mechanical properties. Instead, compatibility between the fluorine-containing seed latex and the acrylic or methacrylic copolymers was emphasized. No mention was made of glass transition temperatures. The single stage acrylic or methacrylic polymerization process lacks the versatility of a two-stage process, where the different stages can be tailored, for example, to emphasize a mechanical or other property on one hand, and cross-linking behavior on the other hand.
Hybrid core-shell latex made by polymerization of some immiscible monomer on a vinylidene fluoride-hexafluoropropylene (FKM-40) seed latex was shown in Chen, Su et al. Colloid Polym. Sci. 2006, 284, 413-421. The polymerization was a single stage acrylic polymerization process. Two-stage acrylic or methacrylic polymerizations were not presented. The ratios of fluoropolymer to acrylic presented ranged from 4-50 wt %, a lower fluoropolymer to acrylic weight ratio than needed for good weathering properties. There was no discussion of glass transition temperatures.
Improved ductility and impact properties of melt-blended polyvinylidene fluoride and acrylic rubber materials that have up to 10 wt % acrylic rubber was shown in Li, Y. et al. Macromolecules 2008, 41, 3120-3124. The acrylic rubber was mechanically dispersed in the polyvinylidene fluoride. Dynamic mechanical analysis and transmittance electron microscopy showed phase-separated behavior between the polyvinylidene fluoride and the acrylic rubber. Glass-transition temperatures below 0° C. were observed. The methods used to make the compositions did not demonstrate a way to make waterborne coatings that provide the improved mechanical properties, and the acrylic rubber composition is unknown other than being acrylic.
Fluoropolymer hybrid compositions are claimed in WO 2010/005756 A1 that are comprised of a fluoropolymer, a first vinyl polymer that is miscible with said fluoropolymer, and a second vinyl polymer having a different composition than said first vinyl polymer and having a Tg of less than 30° C., and optionally other vinyl polymers, where the fluoropolymer dispersion has a minimum film forming temperature of less than 20° C. The compositions are directed toward coatings having a minimum film forming temperature of less than 5° C. and a maximum volatile organic compound content of 50 g/liter without a significant loss of weatherability or dirt resistance. There is no discussion of the mechanical properties of the coatings or what compositions would be advantageous in producing favorable mechanical properties. The first vinyl polymer is required to be miscible with the fluoropolymer, which limits the use of monomers that promote good dampening properties. No mention is made of the glass transition temperature of the first vinyl polymer which, if, higher than 0° C., will give material that embrittles at lower temperatures. A glass transition temperature less than 0° C. for the second vinyl polymer was said to give poor dirt pickup properties, and therefore undesirable.